Our studies are designed to examine the collagen response which accompanies progression and regression of cardiac hypertrophy. The latter will be produced by placement and subsequent removal of a band around the pulmonary artery of cats. Both the duration of banding and time of study after removal of the band will be varied. In addition, active and passive mechanical properties of isolated right ventricular papillary muscles from these animals will be examined and compared with changes in myocardial mass and collagen. We also plan to examine in detailed fashion the concentration-inotropic response of normal and depressed cardiac muscle to acetylstrophanthidin. These studies will be performed using isometrically contracting papillary muscles isolated from the right ventricle of cats. Depressed muscle will be obtained from cats banded for 2-3 weeks. Previous studies in our laboratory have demonstrated that both force development and velocity of shortening are reduced by approximately 50% of normal values at this time period after banding.